Cross-reference to hereby made to Ser. No. 374,588 which is filed concurrently herewith and assigned to the same assignee as the present invention.
The present invention relates to a method or process for determining the concentration of ingredients and other variables in a polymerization process, and, more particularly, the present invention relates to a process for determining the concentration of ingredients and other vairables in a polymerization process by determining the dielectric constant of the polymerization mixture.
Polycarbonates and the process for producing polycarbonates are well known. Generally, such a process comprises reacting a bisaryl carbonate, dihydricphenol, using various types of catalysts in the presence of an organic solvent. Such a process is a batch process. A recitation of such a traditional process, for instance, is to be found in the disclosure of Schnell, U.S. Pat. No. 3,022,272. Recently, a more innovative process has been developed for the production of polycarbonates without the utilization of a solvent. Generally, this process comprises reacting bisphenol-dianhydride with diphenyl carbonate without the presence of a solvent and in the presence of certain metal hydride catalysts containing aluminum hydride or boron hydride ions. Generally, such process comprises mixing the bis(aryl) carbonates and dihydric phenol in the proper proportions and measuring the concentration of the ingredients in the mixture to see that there is the proper concentration of ingredients. Then the catalyst is added to the mixture and the concentration of the catalyst is measured to see that it is within proper concentration. Then, preferably, the different types of stabilizers utilized in such compositions are added, and the concentration of stabilizers that are present in the mixture is measured. The entire mixture is passed through a series of reaction chambers so as to gradually polymerize and form the polycarbonate while at the same time stripping off the by-product phenol. When the polymerization process is completed, the mixture is filtered and is preferably cast into the desired form before it is cooled to form the solid thermoplastic polycarbonate mass. This process is a continuous polymerization process and has many advantages in terms of reducing the cost of labor necessary to produce the finished polycarbonate mass. Some examples of disclosures which relate to such a polymerization process for the production of polycarbonate thermoplastic material without the utilization of a solvent and utilizing the novel metal hydride catalysts are disclosed in the application of Daniel J. Brunelle, Ser. No. 106,856 which was filed Dec. 26, 1979, and which was abandoned as of July 9, 1981, and of which a continuation-in-part is Ser. No. 258,124, which was filed on Apr. 27, 1981, now U.S. Pat. No. 330,664. Other disclosures in this area are that of Brunelle, Ser. No. 106,855, which was filed on Dec. 26, 1979, now abandoned and Brunelle, Ser. No. 134,705, which was filed on Mar. 27, 1980, now U.S. Pat. No. 4,310,656. The patent applications above are given as background. For more details as to the continuous process, reference is to the above patent applications.
The previous process for producing such polycarbonates is a batch process in that all the ingredients are weighed or measured and inserted into a reaction kettle and then the mixture is allowed to react in the proper polymerization degree. The desired polymerization degree was determined by taking out samples every now and then and measuring the intrinsic viscosity of the reaction mixture. By determining the intrinsic viscosity of the reaction mixture, it was possible to determine the molecular weight of the reaction mass and thus the degree of polymerization that had taken place. When there was a sufficient degree of polymerization, the reaction was terminated and the mass of polymerized polycarbonate was filtered to remove impurities and cast in the desired form in which it was to be sold. However, when the instant process was devised as disclosed in the foregoing patent applications, it was desirable that a more rapid means of determining concentration of ingredients as well as the degree of polymerization be used. Thus, in such a continuous process, it was necessary to know if the proper amounts of monomer was mixed together, if the proper amounts of catalysts and stabilizers were mixed into the monomer mixture and if the proper degree of polymerization had taken place at each step along the continuous polymerization process. The only means available to carry out the analysis of the ingredients and degree of polymerization that was known was the use of the intrinsic viscosity measurements for degree of polymerization and for the use of gas chromotography and infrared analysis for the concentration of ingredients and various catalysts and stabilizers. However, such analytical methods, especially the gas chromotgraphy and infrared, were highly undesirable for the continuous polymerization process since this required taking a sample from the process run, taking it to the lab, having it analyzed, and then making the necessary adjustments to the process. Such analytical procedure would keep the process from being truly continuous. Accordingly, it was highly desirable to find a means for measuring such a polymerization process of polymers in a continuous and almost instantaneous manner so that the variable could be determined within seconds at the most, and so that the necessary changes could be made to the process variables. This would allow the proper amount of ingredients to be mixed and the proper polymerization to be carried out in the reaction chambers to produce the desired polymer.
In another vein, the fact that various polymers have various dielectric constants, which can be determined as recognized values, is well known. It is also well known that this dielectric constant of certain thermoplastic and thermosetting polymers would change as the degree of polymerization changed. A discussion of such phenomena is found to be in the publication of Hedwig, entitled Dielectric Spectroscopy of Polymers, John Wiley & Sons, 1977. Note especially Chapters 6 and 7. However, the discussion of Hedwig's is just a broad general commentary without appearing to have any specific information with respect to measuring the variables in a process for producing polymers by determining the dielectric constant of the mixture at various stages in the process. There does not specifically appear to be any discussion of the polymerization of polycarbonates and polyetherimides. Further, there is a disclosure of the determination of the .beta. staging of thermosetting polymers of the measurement of dielectric constants as disclosed in the publication Sanjana, entitled "The Use of Dielectric Analysis in Characterizing the Degree of B-staging and Cure of Composites," International Conference on Polymer Processing, August, 1977, MIT press (1978).
However, this reference does not go into thermoplastic polymers and as stated previously, there is no discussion of polycarbonates of polyetherimides and how the dielectric measurement could be utilized to determine the process variables, that is the concentration of ingredients and degree of polymerization in a continuous polymerization process.
Accordingly, it is one object of the present invention to provide a method for determining the concentration of ingredients in a continuous polymerization process.
It is another object of the present invention to provide a method for determining almost instantaneously the concentration of ingredients in a continuous polymerization process and utilizing such determinations to control the concentration of the mixture.
It is an additional object of the present invention to utilize capacitance measurements to determine and control the concentration of ingredients in a continuous process for producing polyetherimides.
It is yet an additional object of the present invention to provide a method fo almost instantaneously determining the concentration of ingredients and ionic impurities in a continuous polymerization process for producing thermoplastic materials.
It is still a further object of the present invention to almost instantaneously determine the ionic impurities in a mixture of ingredients and the concentration of the ingredients in a mixture of ingredients as well as the degree of polymerization in a continuous polymerization process of thermoplastics by measuring the dielectric constant and dissipation factor.
This and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.